1. Field of the Invention
The invention concerns methods and apparatus for isolating blood serum from coagulated whole blood and blood plasma from mixtures of whole blood with anti-coagulants.
2. Description of the Prior Art
Prior hereto the most widely employed method of separating the liquid phase components from the solid phase components of a blood mixture has comprised centrifugation of the mixture. The serum or plasma is generally then isolated from the solid portion by pipette or decantation techniques. In general, this method does not entirely separate all of the solid particulate matter from the desired serum or plasma. For example, minute particles or shreds of fibrin having a specific gravity approximating the specific gravity of blood serum or blood plasma may not be separated. When the serum is to be subjected to a diagnostic analysis with, for example, an automated electronic analyzer it is important to employ a particulate-free specimen. Fibrin fibers are often the cause of analyzer malfunctions when they clog conduits or orifices in the analyzer.
Filtration has been employed previously to remove solid particles such as minute fibers of fibrin not readily separated by centrifugation. Illustrative of the prior art blood component filtration devices are those described in U.S. Pat. Nos. 3,481,477; 3,512,940 and 3,693,804. Although such filtration devices do isolate the desired blood serum or blood plasma from even microscopic solid particulate matter, they are relatively expensive to construct, requiring extremely close tolerances and seals for operation. They have not been heretofore as widely accepted commercially as the need suggests, because of their cost and difficulty to manufacture. In additon, the prior art filtration devices such as those described in the above patents operate in part by exerting force or pressure upon the blood mixture to be separated. If too great a force is imposed upon the blood mixture, there is a danger that the filtrate will pass through the filter with sufficient velocity to force small particles of solid material through the filter, particularly a resilient filter. The velocity of the filtrate leaving the filter member may also be sufficient to "spray" the filtrate out of the collector device. Furthermore, the necessary force must be applied manually, and only one or two specimens may be process simultaneously, which is an inefficient use of labor. The filtration and isolation procedure with the prior art devices are also generally carried out following separation of the blood components by centrifugation, thereby requiring two distinct steps which consequent extension of time required for total serum preparation.
In contrast, the method of my invention is relatively simple and is activated by readily available and self-limiting gravitational forces. Thus, it enables one to carry out separation, filtration and isolation of the desired blood serum or blood plasma in one convenient centrifugation step. The process is readily applied to a large number of specimens simultaneously, and the centrifugation step is the same operation widely employed in separating serum from clotted blood and cells from mixtures of blood with anti-coagulants. Likewise, the apparatus of my invention is extremely simple in construction and is readily manufactured at low cost since it does not require close dimensional tolerances or seals. The method and apparatus of my invention are particularly useful in the separation of blood serum from clotted whole blood, removing minute particles such as fibrin fibers from their association with the serum isolate.